I've heard the "rule of thumb" one debunked several times. When I first discovered snopes, I thought there would be a page about it - it turned out the be the only UL I knew at the time that didn't have one. Sadly, it's a favorite bludgeon for "men's rights" activists to use against feminists.

I hear that men's rights activists are only allowed to bludgeon feminists with a trope less than the diameter of their penises.